1. Field of the Invention
The invention generally relates to a display apparatus, and more particularly, to a display apparatus having a privacy protecting function.
2. Description of Related Art
Recently, a display apparatus is required to have the characteristics of wide viewing angles when displaying images, so as to comply with the demand that a plurality of users simultaneously watch the images displayed on the same display apparatus. Nevertheless, on certain conditions, such as writing down business information or inputting personal account number and password into an ATM machine, the characteristics of wide viewing angles of the display apparatus may cause the reveal of users' personal information. Accordingly, the display apparatus is required to have the privacy protecting design, so as to prevent others from spying on the highly confidential data.
At present, a privacy protecting design is proposed and achieved by way of the alignment configuration of a liquid crystal display (LCD) panel. In such privacy protecting technology, the LCD panel in the display apparatus serves to perform the display function. Generally, the LCD panel is disposed between two polarizers, while the light-transmission axis directions of the two polarizers are respectively parallel to the column direction and the row direction of the pixel array in the LCD panel. Namely, the light-transmission axis directions of the two polarizers are generally restricted to be at a 0-degree azimuth angle (row direction) and a 90-degree azimuth angle (column direction), respectively, and an included angle between the light-transmission axis directions of the two polarizers is substantially 90 degrees. Meanwhile, the LCD panel is divided into two areas, such as the first area and the second area.
The distribution of the display brightness provided by the first area and the second area of the LCD panel tends to be different at different polar viewing angles and different azimuth viewing angles. Here, the polar viewing angle refers to the included angle between the observation direction of the user and the baseline when the nom al viewing angle direction (defining the 0-degree polar viewing angle) serves as the baseline (i.e., the normal line of the LCD panel), and the azimuth viewing angle refers to the included angle on the horizontal surface between the observation direction of the user and a horizontal axis direction. By applying said design, the LCD panel can perform the privacy protecting function. The brightness distribution in the known LCD panel at different polar viewing angles is described below.
FIG. 1 shows the relationship between the display brightness of a conventional LCD panel in the privacy protecting mode and the corresponding polar viewing angles when images displayed on the LCD panel are observed at various polar viewing angles along the horizontal axis direction (i.e., at the 0-degree azimuth viewing angle or the 180-degree azimuth viewing angle). With reference to FIG. 1, the curve 110 shows the relationship between the display brightness provided by the first area of the display panel and the polar viewing angles when images displayed on the display panel in the privacy protecting mode are observed at various polar viewing angles along the horizontal axis direction, for instance, and the curve 120 shows the relationship between the display brightness provided by the second area of the display panel and the polar viewing angles when the images displayed on the display panel in the privacy protecting mode are observed at various polar viewing angles along the horizontal axis direction. Here, the polar viewing angle in the normal viewing angle direction (i.e., the normal viewing angle) is defined as 0 degree, for instance, and the normal viewing angle represents that the observation direction of the user is perpendicular to the outer surface of the substrate of the display panel. At this time, the normal viewing angle is defined as the 0-degree polar viewing angle, and the outer surface of the substrate of the LCD panel is at the 90-degree polar viewing angle.
As shown by the curve 110 and the curve 120, the brightness of the first area is identical to the brightness of the second area when the observation direction is at the normal viewing angle (i.e., the 0-degree polar viewing angle). Accordingly, the user can observe the clear display images if both eyes of the user receive the display images at the normal viewing angle. By contrast, at the polar viewing angle V1, the display brightness of the first area is relatively low, while the display brightness of the second area is relatively high. Therefore, the user who watches the display image at the polar viewing angle V1 can merely observe the unclear images, and thereby the privacy protecting effects can be achieved. In other words, the image data obtained by both eyes of the user at the polar viewing angle V1 are less sufficient than the image data obtained by both eyes of the user at the normal viewing angle. The user needs to watch the images in the normal viewing angle direction to obtain the complete and clear image data, and others who watch the images in the side viewing angle direction can only obtain the unclear images or the incomplete image data. Therefore, the aforesaid privacy protecting mode can be referred to as a narrow viewing angle display mode.
It should be mentioned that the first area and the second area have the same display brightness when the polar viewing angle is 0 degree, as shown by the curve 110 and the curve 120. Due to the fact that both eyes of the user are separated from each other by a distance, the viewing angle at which the user observes the display images on the display panel in the normal viewing angle direction may actually range from an angle V2 to an angle V3, e.g., within the range of the 0-degree normal viewing angle ±5 degrees. That is to say, the user located in the normal viewing angle direction observes the display images on the LCD panel at the angles around the normal viewing angle rather than right at the normal viewing angle. At this time, the brightness of the first area differs from the brightness of the second area, and thereby the user who watches images at the normal viewing angle may feel dizzy. In summary, although the privacy protecting mode, i.e., the narrow viewing angle display mode, can preclude the reveal of personal information, the privacy protecting mode discomforts the user located in the normal viewing angle direction.